RE: ASM - number of LUNS rule of thumb
- From: Luca Canali <Luca.Canali@xxxxxxx>
- To: "George.Johnson@xxxxxxx" <George.Johnson@xxxxxxx>
- Date: Thu, 12 Aug 2010 09:34:45 +0200
Hi George,
LUNs to be used for ASM cannot be larger than 2TB, a technology limitation, so
this will also set a minimum number for the LUNs you will need, depending on
the size of your DB.
Our experience is with using ASM and normal redundancy on low-cost storage, in
that case one would export 1 LUN per disk (JBOD config) so we have systems with
more than 100 LUNs and having a large number of LUNs does not seem to be a
problem for Oracle or Linux. When using external (RAID) redundancy I imagine
one prefers to minimize the number of exported LUNs for simplicity as most
details are taken care at the storage level. Anyway details will vary depending
on how the storage is set up, so it's hard to give a general recommendation, I
believe.
One large DATA and FRA diskgroups are easier to manage, and also ASM is stable
and mature enough that it reasonably allows for such an architecture. Also if
you have a single host (no clustering?) I would say you have to think globally
about your HA requirements and in that picture consider the risk of an
ASM/storage-related issue blocking all your DB activities on the given node.
Having said that the day you will have a corruption on one diskgroup, if ever,
you'll probably very much prefer to have gone for the solution of having
multiple diskgroups :)
Cheers,
L.
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Johnson, George
Sent: 11 August 2010 17:13
To: oracle-l@xxxxxxxxxxxxx
Subject: ASM - number of LUNS rule of thumb
I wanted to ask the list some advice on a particular ASM
"rule-of-thumb" and advice on diskgroups per host.
We have recently decided upon using ASM, yes I know late to the
party, we have studied quite a few white papers and they often suggest
that you start somewhere between 4 to 8 luns maximum per diskgroup as a
rule-of-thumb. I don't like rules-of-thumb, they suggest that no-one has
any idea and it's a best guess! What do others have as a starting point
basis for the number of raw luns under each diskgroup and why that
number? I appreciate there are many more factors involved and we are
slowly working through lots of these, but I am trying to get some facts
based on experience, rather than simply taking documented suggestions as
gospel truth.
Additionally, my colleague and I are arguing over the merits of
the number of diskgroups per host. Say you have 4 instances on a host,
does each instance have at least two diskgroup each ( DATA+FRA for
example) , or do you simply make big diskgroup and throw all the
instances into it? The "all-in-one" options suggest 'eggs-in-one-basket
to me though.
Any advice from your vast collective experience on these two
points, would be greatly appreciated.
Rgds
George Johnson
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